Computer Science
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996m%26ps...31...60s&link_type=abstract
Meteoritics and Planetary Science, Vol. 31, p. 60-72 (1996)
Computer Science
18
Scientific paper
The isotopic composition and concentrations of noble gases were measured in the eucrites Bereba, Cachari, Caldera, Camel Donga, Chervony Kut, Ibitira, Jonzac, Juvinas, Millbillillie, Moore County, Padvarninkai, Pasamonte, Pomozdino, Serra de Mage, Sioux County, and Vetluga. The distribution of 81Kr-Kr exposure ages shows "clusters" at (7±1) Ma, (10±1) Ma, (14±1) Ma, (22±2) Ma, and (37±1) Ma that agree with those for howardites, eucrites, and diogenites (HED) at (6±1) Ma, (12±2) Ma, (21±4) Ma, and (38±8) Ma. This most likely indicates a common origin of HED meteorites. Correlation equations for the shielding-sensitive cosmogenic ratios 78Kr/83Kr, 80Kr/83Kr, 82Kr/83Kr , and 124Xe/131Xe were obtained.
Comparison with data from simulation experiments suggests that most eucrites were exposed to the cosmic radiation as somewhat large meteoroids with diameters of 1 m or more. The shielding-dependence of the 78Kr and 126Xe production rates was found to be small, with a few exceptions the variations are <10%-15%. Concentrations of spallogenic 3He indicate diffusive losses of up to 70% that can be, in First approximation, described by a model of quasi-continuous losses during the exposure to the cosmic radiation with a loss rate of the order of ˜3 x 10-8 a-1. Radiogenic 4He shows additional substantial losses that occurred at the time of, or prior to, the separation of the meteoroids from their parent body. Typical 40Ar retention in eucrites is 50%-60% which corresponds to a 40Ar-K retention age of 3.4-3.6 Ga. In all analyzed unbrecciated eucrites, the retention is distinctly larger (70%-100%). The 244Pu fission ratio (86Kr/136Xe)Pu, was evaluated from the data on Pomozdino samples to be 0.039±0.014.
Begemann Friedrich
Shukolyukov Alex
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